Article pubs.acs.org/jced
Vapor−Liquid Equilibria of the Binary System 1,5-Hexadiene + Allyl Chloride Sona Raeissi,† Louw J. Florusse,‡ and Cor J. Peters*,§,∥ †
School of Chemical and Petroleum Engineering, Shiraz University, Mollasadra Ave, Shiraz 71345, Iran Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands § Chemical Engineering Department, The Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emirates ∥ Department of Chemical Engineering and Chemistry, Separation Technology Group, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands ‡
ABSTRACT: Knowledge of accurate vapor−liquid equilibrium data for mixtures of allyl chloride and 1,5-hexadiene is important for several industrial purposes. The bubble points of binary mixtures of allyl chloride and 1,5-hexadiene have been measured experimentally using a synthetic method. Measurements were carried over concentrations ranging from (0 to 1) mol % of allyl chloride. The vapor−liquid equilibrium is presented at temperatures ranging from (25 to 100) °C. Within this temperature range, bubble-point pressures up to 5 bar were observed. The experimental results indicated that, as the concentration of allyl chloride increases in the mixture, higher pressures are necessary for a complete dissolution of the two components. In addition, solubility pressures increase as temperature increases for a mixture of fixed composition.
1. INTRODUCTION Allyl chloride, also known as 1-chloro-2-propene, 3-chloropropene, 3-chloropropylene, and chloroallylene, is an important raw material for the production of dichlorohydrin. Allyl chloride is, itself, produced by the chlorination of propylene. However, the product is only (75 to 80) % allyl chloride, which needs to be purified. Hexadienes make up the major part of the impurities, but smaller amounts of other aliphatic and cycloaliphatic hexene and hexadiene isomers are also present, such as normal hexenes, methylpentenes, methylcyclopentenes, and methylcyclopentadienes.1 Purification is generally performed by distillation, in at least two steps.1 In the final purified product, (0.3 to 1.0) wt % hexadiene is still present. When dichlorohydrin is produced with an allyl chloride that contains such amounts of hexadiene impurities, undesirable chlorinated organic byproducts are produced. This results in excess costs to purify the aqueous effluents leaving the plant. It has been shown that, if an allyl chloride feed containing less than 0.3 wt % hexadiene is used with water and chlorine to produce dichlorohydrin, much less undesirable byproducts are produced, and much less purification costs are necessary.1 Apart from the above, one of the processes to produce 1,5-hexadiene involves a one-step Grignard-type process. The process involves contacting magnesium metal with a mixture comprising of allyl chloride.2 For example, Turk and Chanan3 presented a process for preparing 1,5-hexadiene by the reaction of allyl chloride in anhydrous ether with magnesium turnings.2 These are examples of two different processes which involve allyl chloride and 1,5-hexadiene in the process mixture. © 2013 American Chemical Society
The optimum design and operation of such processes requires knowledge of the phase behavior of the components involved. A study by Giles and Wilson4 is the only literature publication that presents experimental data on the system 1,5-hexadiene + allyl chloride. However, the mentioned study includes data for only two isotherms. In this study, we have extended the experimental data on this binary mixture by measuring the bubble points of a number of isopleths, extending over a wide range of temperatures.
2. EXPERIMENTAL SECTION The Cailletet equipment, which operates according to the synthetic method, was used to carry out the experiments (see Figure 1). Dosed mixtures of allyl chloride and hexadiene were injected into a Pyrex equilibrium cell, called the Cailletet tube, with a length of about 500 mm and inner and outer diameters of 3 mm and 10 mm, respectively. This fixed (and known) concentration remains constant throughout the whole experiment as no samples are ever taken out from the equilibrium tube. The temperature of the sample is set to a desired value using thermostat liquid which circulates around the equilibrium tube. The pressure on the sample is adjustable, using a screwtype hand pump. In this manner, phase transitions for a sample of fixed overall composition at a set temperature can be observed visually by gradually changing the pressure. In this Received: August 19, 2013 Accepted: December 9, 2013 Published: December 20, 2013 52
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Figure 1. Schematic representation of the Cailletet apparatus: A: autoclave, B: magnets, C: capillary glass tube, D: drain, E: motor, F: metal stirrer, G: platinum resistance thermometer, H: rotating hand pump, Hg: mercury, I: thermostat liquid in, L: line to dead weight pressure gauge, M: mixture being investigated, Ma: manometers, O: thermostat liquid out, Or: hydraulic oil reservoir, P: closing plug, R: Viton-O-rings, S: silicone rubber stopper, T: mercury trap, Th: glass thermostat, V: valve.5
study, pressure is first reduced until two phases, namely, vapor and liquid, are observed. Then the pressure is slowly increased until the last bubble of vapor disappears. This marks the bubble point at the set temperature. The composition of the liquid phase is assumed to be equal to the overall composition injected into the equilibrium cell. To ensure equilibrium, the sample is mixed with a steel ball which moves by two reciprocating magnets positioned adjacent to the equilibrium tube. The pressure is measured using a Budenberg dead-weight pressure gauge. The thermostat liquid is maintained within a constancy better than 0.01 K using a thermostat bath. A platinum resistance thermometer is used to record the temperature with a maximum error of 0.02 K. Depending on the thermostat liquid used (e.g., ethanol, water, or silicon oil), a temperature range of (250 to 450) K is achievable. The Cailletet apparatus and measuring procedures were explained in detail in earlier publications.5−7 The chemicals used, their suppliers, and their purities are presented in Table 1. These substances were used without further purification. The structures of 1,5-hexadiene and allyl chloride are shown in Figure 2.
Figure 2. Chemical structures of 1,5-hexadiene (left) and allyl chloride (right).
3. RESULTS AND DISCUSSION Experimental bubble point pressures of binary mixtures of 1,5hexadiene + allyl chloride were measured within a temperature range of (25 to 100) °C for various molar concentrations of the mixture ranging in between each pure axis. The bubble-point pressures were determined up to pressures of about 5 bar. The experimentally measured data are presented in Table 2 and Figure 3. As temperature increases, higher pressures are required to dissolve 1,5-hexadiene into allyl chloride. Since data in the form of isothermal bubble point curves over a range of concentrations are usually more useful in research, the measured isopleths have also been interpolated into the form of P−x data at various temperatures. These values are given in Table 3. Figure 4 shows that bubble-point pressures decrease as the concentration of 1,5-hexadiene increases in the mixture. To the best of our knowledge, there is only one other study in literature which has presented experimental bubble-point data on this system.4 However, the overlap of their data with the ones measured in this work is only at one isotherm, namely, at 333.15 K. The data of both studies are compared in Figure 5. It is seen that the bubble-point pressures measured in the present study are slightly higher.
Table 1. Suppliers and Purities of the Chemicals chemical name
source
purity, weight percent
1,5-hexadiene allyl chloride
Janssen Chimica Janssen Chimica
> 98 % > 99 % 53
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Table 2. Experimental Bubble-Point Data of Temperature T, Pressure P, and Liquid Mole Fraction x for the System 1-5Hexadiene (1) + Allyl Chloride (2)a x1
T/K
P/MPa
T/K
P/MPa
T/K
P/MPa
0.000
298.88 323.13 333.47 352.30 369.15 303.29 333.05 362.75 303.43 333.21 362.93 303.33 333.04 353.12 303.41 333.04 353.00 313.05 342.76 369.36
0.055 0.125 0.173 0.294 0.454 0.066 0.171 0.385 0.066 0.171 0.381 0.063 0.164 0.288 0.068 0.163 0.283 0.056 0.147 0.303
308.19 323.19 343.12 353.05
0.075 0.126 0.228 0.301
313.35 323.75 343.83 363.03
0.090 0.126 0.233 0.389
313.11 342.86 369.59 313.08 343.21 369.23 313.07 337.38 362.91 313.29 337.99 363.04 322.92 352.84
0.092 0.227 0.455 0.091 0.227 0.447 0.088 0.189 0.371 0.089 0.19 0.366 0.078 0.197
322.96 352.82
0.126 0.298
323.11 353.18
0.125 0.298
323.05 342.85 369.96 323.39 342.65 370.85 333.00 362.75
0.122 0.218 0.441 0.123 0.214 0.442 0.109 0.256
0.057
0.115
0.218
0.297
a
Figure 4. Solubility of 1,5-hexadiene (in mole fraction) in allyl chloride at six different temperatures: +, T = 313.15 K; red −, T = 323.15 K; green , T = 333.15 K; ◆, T = 343.15 K; ■, T = 353.15 K; and ▲, T = 363.15 K. The solid curves are predictions by the Peng− Robinson equation of state at each temperature, with kij = 0 and lij = 0.
Figure 3. Experimentally measured bubble-point pressures vs temperature for the 1,5-hexadiene (1) + allyl chloride (2) binary system for six different molar concentrations: ◇, x1 = 0.000; □, x1 = 0.057; +, x1 = 0.115; ×, x1 = 0.218; ○, x1 = 0.297; and △, x1 = 1.000.
The second row of data in Table 3, corresponding to a hexadiene molar fraction of 0.057, hints at azeoptropic phase behavior since the pressures at this concentration are slightly higher than the two adjacent measured concentrations for the three lowest temperatures in the table, indicating a “maxima” in the Px diagram, typical of azeotropic behavior. However, since the pressure differences between these very “minor” maxima and the neighboring points are at maximum equal to 0.003 MPa, falling within the experimental error range of pressure, it would be inaccurate to make a definite conclusion of azeotropic behavior for this system. In other words, these minor peaks may either be indicative of the beginnings of azeotropic behavior, or else, they may simply be the result of experimental scattering of data. The data of Giles and Wilson at 333 K on this same binary mixture did not indicate any azeotropic behavior, which is a further caution against concluding that this system has azeotropy. The phase behavior of this system was predicted using the Peng−Robinson equation of state8 using the classical quadratic (van der Waals 1) mixing rule.9 No binary interactions were considered (kij = 0 and lij = 0) in order to investigate the predictive capability of a typical engineering cubic equation of state for this binary system. The critical properties used in the modeling are given in Table 4. The results of these predictions
1.000
Standard uncertainties u are u(T) = 0.02 K, u(x1) = 0.005, and u(P) = 0.01 MPa.
Table 3. Isothermal Solubility Data of Liquid Mole Fraction x, Temperature T, and Pressure P for 1,5-Hexadiene (1) in Allyl Chloride (2)a P/MPa
a
x1
313.15 K
323.15 K
333.15 K
343.15 K
353.15 K
363.15 K
0.000 0.057 0.115 0.218 0.297 1.000
0.089 0.092 0.091 0.088 0.089 0.056
0.125 0.127 0.126 0.122 0.121 0.079
0.171 0.172 0.171 0.166 0.164 0.109
0.229 0.229 0.227 0.220 0.218 0.149
0.301 0.301 0.297 0.289 0.284 0.198
0.390 0.389 0.384 0.373 0.366 0.259
Standard uncertainties u are u(T) = is 0.02 K, u(x1) = 0.005, and u(P) = 0.01 MPa. 54
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +971 2 607 5492. Fax: +971 2 607 5200. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS S. Raeissi is thankful to Shiraz University and Eindhoven University of Technology, and in particular to Prof. Maaike Kroon, for facilitating this collaboration.
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Figure 5. Comparison of bubble-point pressures of 1,5-hexadiene (1) + allyl chloride (2) measured in this work and by Giles and Wilson4 at 333.15 K.
Table 4. Properties of 1,5-Hexadiene and Allyl Chloride Used in the Equation of State Modeling4 component
Tc/K
Pc/MPa
ω
1,5-hexadiene allyl chloride
508.0 514.15
3.350 4.710
0.2259 0.1478
REFERENCES
(1) De Jong, A. W.; Nisbet, T. M. Purification of allyl chloride. Patent US5723703 A, 1998. (2) Bank, H. M.; Hayes, I. K. Q. Process for the preparation of 1,5hexadiene. Patent EP 0729931 A1, 1996. (3) Turk, A.; Chanan, H. Biallyl. Org. Syn. 1947, 27, 7−8. (4) Giles, N. F.; Wilson, G. M. Vapor-liquid Equilibria on Seven Binary Systems: Ethylene oxide + 2-methylpropane; Acetophenone + Phenol; cw-l,3-dichloropropene + 1,2-dichloropropane; 1,5-hexadiene + Allyl chloride; Isopropyl acetate + Acetonitrile; Vinyl chloride + Methyl chloride; and 1,4-butanediol + γ-butyrolactone. J. Chem. Eng. Data 2006, 51, 1954−1962. (5) Raeissi, S.; Peters, C. J. Experimental Determination of HighPressure Phase Equilibria of the Ternary System Carbon Dioxide + Limonene + Linalool. J. Supercrit. Fluids 2005, 35, 10−17. (6) Raeissi, S.; Peters, C. J. Bubble Point Pressures of the Binary System Carbon Dioxide + Linalool. J. Supercrit. Fluids 2001, 20, 221− 228. (7) De Loos, T. W.; Van Der Kool, H. J.; Ott, P. L. Vapor-Liquid Critical Curve of the System Ethane + 2-Methylpropane. J. Chem. Eng. Data 1986, 31, 166−168. (8) Peng, D. Y.; Robinson, D. B. A New Two Constant Equation of State. Ind. Eng. Chem. Fundam. 1976, 15, 59−64. (9) Raeissi, S.; Peters, C. J. Simulation of Double Retrograde Vaporization using the Peng−Robinson Equation of State. J. Chem. Thermodyn. 2003, 35, 573−581.
are shown in Figure 4 as solid curves. It is seen that deviations increase at higher temperatures. This is to be expected, since systems deviate further from ideality as their temperatures are increased, that is, as they move closer toward their critical state.
4. CONCLUSIONS Bubble-point pressures were determined experimentally for binary mixtures of 1,5-hexadiene + allyl chloride. Results indicated that this binary system may possibly have azeotropy at the lower temperatures investigated, although no definite conclusions could be made. It was shown that higher pressures are required to solve increasing amounts of allyl chloride in hexadiene. Increased pressures were also necessary for a complete dissolution of the components in one another at higher temperatures. The simple cubic Peng−Robinson equation of state seems to be applicable for modeling the phase behavior of this system, especially at lower temperatures where even the predictive mode of the equation does not deviate too much from experiments. However, at higher temperatures, it is suggested to incorporate binary interaction parameters, which are fit to the experimental data, for more accurate correlations. The quantitative data obtained in this study on solubilities at different temperatures and pressures can assist in feasibility studies on future processes and separation techniques involving these substances, as well as the optimizations of current processes. A point that should be highlighted is that separations based on vapor−liquid equilibria are restricted by azeotropic behavior, and since this binary mixture may possibly be at the verge of azeotropic behavior, special precautions and considerations must be taken into account when designing/optimizing such separation processes involving these two components within low concentration ranges of 1,5-hexadiene. This concern is even more urgent at lower temperatures. 55
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